With MRI, a high field magnet, typically superconducting, is arranged in a torus configuration and with the patient lying down inside the magnet on a table where the magnetic field allows a pulsed and sequenced magnetic and EM field to probe the body to produce images, which allow the trained radiologist to determine with high probability the anatomy of the patient. MRI techniques are very good at detecting the anatomical location of different diseases, for example, tumours.
The magnet for highest field strength is generally cylindrical with the patient lying along the bore but other magnet shapes and arrangements are used in lower strength configurations.
Most MR imaging is carried out on a diagnostic basis where the patient is placed on a diagnostic table which moves into the bore and carries the patient to a required position. In these cases the patient is normally conscious and thus can be moved to the required location on the table so that, when the table enters the bore, the part of the patient to be imaged is located relative to the table so that it enters the bore at the field of view of the MR system, generally at the center of the bore on the axis. In most cases therefore the table is movable only longitudinally of the bore to move the patient into and out of the bore.
The table also is prevented from any significant movement relative to the bore since it includes mechanical structures which fill the available part cylindrical area underneath the surface of the table.
In U.S. Pat. No. 5,735,278 (Hoult et al) issued Apr. 7, 1998,disclosed a medical procedure where a magnet is movable longitudinally relative to the table and to the patient on the table. The moving magnet system allows intra-operative MRI imaging to occur more easily in neurosurgery patients, and has additional applications for liver, breast, spine and cardiac surgery patients. The table is set up for the required surgery and the magnet is moved into place over the table to effect the imaging. The table can tilt about a transverse axis and rotate about a longitudinal axis.
Related disclosures are made in U.S. application Ser. No. 12/333,032 filed Dec. 11, 2008 and Ser. No. 12/420,859 filed Apr. 8, 2009 by the present Assignees, the disclosures of which are incorporated herein by reference, which correspond to PCT Applications CA/2009/000672 and CA/2009/00673 filed May 25 2009, to which reference may be made for further detail.
U.S. Pat. No. 7,319,325 (Petot) issued Jan. 15, 2008 and assigned to Philips claims the use of a position sensor to provide feed back to the drive system of a table within the bore of an MRI magnet. The movement as disclosed appears to be simply linear movement along the bore.
U.S. Pat. No. 7,486,076 (Nagao) issued Feb. 3, 2009 and assigned to Ricoh or Hitachi discloses moving the table based on information relating to the difference between the actual position and a desired position. Movement in a second direction at right angles to the longitudinal direction is possible during whole body scanning.
U.S. Pat. No. 6,822,447 (Yamagata) issued Nov. 23, 2004 and assigned to Toshiba discloses moving the table in two directions to move the point of interest to the required imaging position in the magnet.
U.S. Pat. No. 6,045,262 (lgeta) issued Apr. 4, 2000 and assigned to Hitachi discloses a table which is used in X-ray and MRI which can be moved in two directions.
Published US Patent Application 2005/0154291 (Zhao) published Jul. 14, 2005 discloses a table which is used in MRI which can be moved in two directions and tilted during imaging in the magnet.